1. Field of the Invention
This invention relates to a synchrotron radiation technique using a synchrotron or SOR (Synchrotron Orbital Radiation), and more particularly to a synchrotron radiation apparatus that enlarges radiation area by oscillating the radiation reflecting mirror.
2. Description of the Related Art
Up to now, it has been common practice to use photolithography apparatus to form LSI patterns. As LSI patterns are getting much smaller, however, photolithography apparatus are becoming less suitable for producing such finer LSI patterns. To cope with this situation, X-ray lithography apparatus have recently been developed which can produce even finer patterns. They require an X-ray source of high intensity and as such a source, SOR is now attracting attention.
In a conventional X-ray lithography apparatus using SOR as the X-ray source, an SOR-caused X-ray beam reflects at the X-ray reflecting mirror, passes through the X-ray beam window, and meets the X-ray mask. The X-rays passing through the X-ray mask fall upon the wafer to replicate the mask pattern into the wafer. Here, the spot size of the X-ray beam from SOR is, for example, a rectangle of approximately 5 mm.times.25 mm. To use this X-ray beam as lithography light in semiconductor manufacturing apparatus, it is necessary to enlarge the X-ray illumination area to a square of approximately 25 mm.times.25 mm equal to the exposure area. Such enlargement of the X-ray illumination area is achieved by oscillating the mirror.
However, this type of apparatus has the following problem: That is, the X-ray beam window, which separates the SO beam line from the exposure chamber (the ordinary working area), is generally made up of beryllium thin film. To strengthen the X-ray beam window which has the size 25 mm.times.25 mm or more large enough to cover the exposure area, so that the window can withstand the pressure difference between the high vacuum beam line and the chamber of atmospheric pressure or low vacuum, it is necessary to thicken the beryllium thin film. Since beryllium has not a very large X-ray transmittance, thicker beryllium film involves larger attenuations in X rays, which makes the exposure time longer, thus decreasing the overall throughput.
As noted above, in SOR-based X-ray radiation techniques, the enlargement of the X-ray illumination area is achieved by oscillating the X-ray reflecting mirror. However, making the X-ray beam window size larger to assure an enough exposure area requires the beryllium thin film to be thicker, resulting in a larger X-ray attenuation. Further, in X-ray lithography apparatus, such larger X-ray attenuation lowers the overall throughput.